The present invention relates to a magnetic disk driving apparatus for recording information on a magnetic disk.
A magnetic disk driving apparatus is, for example, a hard disk drive generally used in a computer.
The bearing of a conventional magnetic disk driving apparatus is a ball bearing, and rotation of the magnetic disk is supported by the ball bearing. Accordingly, the magnetic disk cannot be rotated at high precision. To solve this problem, a magnetic disk driving apparatus using a dynamic pressure fluid bearing has been developed.
In positioning of a magnetic head, high precision positioning of the magnetic head is difficult due to vibration of the ball bearing, whereas high precision positioning of a magnetic head is possible in a magnetic head driving apparatus using a dynamic pressure fluid bearing.
In a recent magnetic disk driving apparatus, the magnetic resistance effect type magnetic head (hereinafter called MR magnetic head) is used for reduction of size of the apparatus main body and high density recording.
However, due to friction between the magnetic disk rotating at high speed and the air, the magnetic disk is electrostatically charged, and a potential difference occurs between the magnetic disk and the magnetic head. If discharge occurs by this potential difference between the magnetic disk and the MR magnetic head, the magnetic resistance effect thin film for composing the MR magnetic head is broken.
To solve this problem, various discharge countermeasures are proposed as earth means of a magnetic disk driving apparatus. These proposals may be summarized as follows.
(1) Earth means of magnetic head
As disclosed in Japanese Laid-open Patent No. 4-137212, a conductive layer of the grounding potential is disposed outside of the MR magnetizing area of the magnetic head slider, and the earth means discharges the charged static electricity through this conductive layer. As disclosed in Japanese Laid-open Patent No. 2-94103, the central potential and reference potential of the MR magnetic head are set at desired potentials, and the current discharged by the capacitor between the MR magnetic head and magnetic disk is kept to a small value by this means.
(2) Earth means between motor shaft and apparatus housing
As disclosed in Japanese Laid-open Utility Model No. 1-31597, a ball preloaded with a spring is provided in the shaft. The ball is brought into contact with the bump of the apparatus housing by this earth means.
(3) Earth means for sliding a contactor fixed in a housing at a motor shaft end.
As disclosed in Japanese Laid-open Patent No. 7-176132 or Japanese Laid-open Patent No. 7-254213, the earth means is composed of a contactor positioned outside of the housing and sliding with the end of motor shaft, and a leaf spring having an electrode with the base end side fixed to the housing, and the leading end side sliding with the contactor.
(4) Earth means of motor shaft and hub
As disclosed in Japanese Laid-open Patent No. 5-81825, the earth means fits a finger such as a leaf spring to the outer circumference of the shaft to slide, as disclosed in Japanese Laid-open Patent No. 5-288214. According to the earth means, a ball preloaded with a spring is provided in the shaft, and the ball slides while abutting against the hub. Alternatively, as disclosed in Japanese Laid-open Patent No. 7-32746, in this earth means, a cylindrical protrusion is provided in a rotating hub, and the cylindrical protrusion is put in a magnetic fluid charged in the shaft.
(5) Earth means of lubricant of dynamic pressure bearing
As disclosed in Japanese Laid-open Patent No. 5-347066, the earth means uses conductive magnetic fluid as lubricant of the dynamic pressure bearing, and as disclosed in Japanese Laid-open Patent No. 1-77125 or Japanese Laid-open Patent No. 7-6491, the earth means uses conductive lubricant as lubricant of the dynamic pressure bearing.
(6) Earth means of ball bearing
As disclosed in Japanese Laid-open Utility Model No. 3-91067, the earth means uses conductive grease as the grease used in the ball bearing.
However, as in (1), in the case of the earth means for preventing discharge breakdown by disposing a special circuit at the magnetic head side only, the cost is very high, and the head mechanism is complicated.
In the earth means in (2) to (4), to prevent discharge breakdown at the motor side, the structure of the magnetic disk driving apparatus is desirably modified.
In the magnetic disk driving apparatus using dynamic pressure fluid bearing high in capacity, since the lubricant is used in the tightening area of the member rather than in the magnetic disk driving apparatus having the ball bearing. Since only conductive lubricant or conductive magnetic fluid is used as the lubricant for the dynamic pressure bearing in (5), the resistance between the magnetic disk and housing (or motor housing) is high. Thus, the problem of discharge breakdown is not solved.
A magnetic disk driving apparatus of the invention comprises:
(a) a motor including a shaft having a rotor and a bearing fitted to the shaft,
(b) a housing accommodating the motor and forming a hole,
(c) a magnetic disk disposed in either one of the shaft and the bearing, and
(d) a conductive adhesive for connecting at least one pair selected from the group consisting of
(i) the hole of the housing and the bearing,
(ii) the hole of the housing and the shaft, and
(iii) the bearing and the shaft,
in which the magnetic disk and the housing are conducting electrically to each other.
In this constitution, without requiring modification of the motor structure, it is possible to conduct between the magnetic disk and the housing by lowering the electric resistance between the magnetic disk and the housing of the apparatus main body.
By such electric conduction between the magnetic disk and the housing, the electric charge generated in the magnetic disk rotating at high speed can be released to the housing.
As a result, discharge breakdown of the magnetic head is prevented, and destruction of the information recorded in the magnetic head can be prevented.